The overall effect was a little like going to the gym with his brain. He did not notice any manifest change at first, but by the end of it he found himself with new powers of observation and retention.

“They really fine-tuned skills I never thought I had,” he says.

He was then ready to join part of a larger intelligence and counterterrorism effort that Commissioner Raymond Kelly had initiated in the aftermath of 9/11. The NYPD had learned that it could not count on the federal government to protect the city of New York.

That long and unnerving lesson had begun after the assassination of Rabbi Meir Kahane of the Jewish Defense League in the ballroom of a Manhattan hotel in 1990. City detectives afterward seized two file cabinets from the Brooklyn apartment of a prime suspect. The detectives transported the evidence to their squad room and stepped out for dinner. They returned to discover that the FBI had taken the cabinets before they could study what was inside. The contents included drawings of the World Trade Center and a paper bearing the words “al Qaeda.”

But the FBI did not get around to translating the stuff in the files until after the first bombing of the World Trade Center in 1993, during Kelly’s first tenure as police commissioner. The bombers included at least one of the conspirators in the Kahane killing and several other militants long known to the FBI. An informant had alerted the FBI that these individuals were in the midst of a major bomb plot. There is some speculation that the bombing was carried out with a timing device supplied by the informant. There is no disputing that an FBI supervisor ordered the agents to break off contact with the informant shortly before the bomb was readied.